The invention relates to line-of-sight optical communications. Prior art includes many examples fitting the general category. In a typical example, a first light emitter directs light toward a remote optical receiver. Near the receiver location, a second emitter directs light toward an optical receiver associated with the first emitter. First and second emitters are provided with a means of modulating the emitted light so that information is transmitted back and forth between first and second emitter locations. Additional features that are well known in the art include;    1) means of adjusting the direction of transmitting and receiving elements to achieve maximum bidirectional coupling efficiency,    2) use of a retro-reflector and means of modulating light passing through retro-reflector to eliminate the requirement for a second emitter, and    3) means of tracking the motions of one or both receiver locations to maintain high coupling efficiency in the presence of such motions.
When line-of-sight optical communications according to prior art is employed on moving platforms, certain deficiencies become evident;    1) means of stabilizing the platform is required in order to minimize loss of bidirectional tracking,    2) tracking failures occur frequently and require substantial time for re-acquisition,    3) distance measurement between communicating units is not continuously updated, and    4) platform vibration degrades signal quality.